The present invention relates to a safety valve arrangement for an apparatus operating with a pressure medium having a pressure medium input and a pressure medium output which are connected to each other by a valve. The valve has a valve seat and a valve closing element which can be moved towards and away from the valve seat. The valve closing element is held by a spring arrangement and goes from a first end position to a second end position in which the valve is open when the force of the pressure medium acting upon the valve closing element overcomes the opposing force of the spring arrangement acting upon the valve closing element.
A safety valve arrangement of this type is known from EP 0 357 420 B1 (U.S. Pat. No. 4,856,555).
The known safety valve arrangement has a housing with a pressure medium input and a pressure medium output. The pressure medium input and the pressure medium output can be shut off from each other by a valve. The valve comprises a valve seat and a valve closing element moveable relative to the valve seat. The valve closing element is held by a Belleville spring washer in a first end position in which the valve is closed. The closing element goes to a second end position in which the valve is open when the force of the pressure medium acting upon the valve closing element overcomes the opposing force of the Belleville spring washer acting on the valve closing element.
In a safety valve arrangement of this type, the opening of the valve occurs in a creeping fashion. This means that the valve closing element is pushed at a relatively slow pace by the pressure building up in the pressure medium input away from the valve seat in the opening direction of the valve. It is possible that sufficient pressure may not build up in order to bring the valve closing element completely into the open position. A small gap between the valve seat and the valve closing element may result in a "creeping permeability." If such a safety valve arrangement is used in a compressed-air supply system containing a compressor, the permeability may lead to charring at the valve seat and thereby to interference with the safety valve arrangement. For example, charring at the valve seat may be produced by the deposit of oil particles present in the compressed air, or by temperature-dependent changes in the oil-moistened valve surfaces.
Combination of the known safety valve arrangement described above with a compressor may have the result that although the valve closing element may briefly reach its open position when a predetermined pressure level has been exceeded, it does not remain in its open position due to pressure fluctuations at the pressure medium input of the safety valve arrangement. These fluctuations may be caused by pressure pulsations.
It is therefore an object of the present invention to provide a safety valve arrangement of the type initially mentioned, wherein the valve is brought rapidly and completely into its open position when a certain pressure has been exceeded.